Electron image tube



Nov. 7,- 1939. E. BRUCHE El AL 2,179,083

ELECTRON IMAGE TUBE Filed Aug. 13, 1937 INVENTORS ERNST BRUCHEAND 2/ 23 BY MUERSCHAFFERN/Cl/T :TTQQNEY Patented Nov. 7, 1939 UNITED-STATES Artur ELECTRON IMAGE TUBE Application August 13, 1937, Serial No. 158,880 In Germany August 8, 1936 3 Claims. cram-165i,

This invention relates to an electron'optical reproducing system consisting only of cathode and anode and in which through suitable shape and arrangementof these two electrodes care is taken that the potential field for the reproduction has favorable properties. Such a system was used for image converters and it was found that it is possible to reproduce a large region of the oathode, constructed as a photo-cathode with great sharpness and without distortion. A tube of this type is shown inthe paper entitled: Fortschritte auf dem Gebiet der geometrischen Elektronenoptik in Jahrbuch des Forschungsinstituts der AEG volume 4 (Berlin 1936), pages 45-46.

The invention will be described in detail making reference to the drawing in which Fig. 1 shows a tube having a spherical cathode and an anode with appropriate leads to supply potentials for purposes of describing the invention,

Fig. 2 shows one embodiment of our invention in which the spherical cathode shown in Fig. 1 is replaced by a non-spherical surface of revolution, and

Fig. 3 shows a modification of the embodiment of our invention shown in Fig. 2. Y

The construction of such image converter tube can be seen in the above identified paper, Fig. 18, on page 32 or in the paper by Schafiernicht in the Zeitschrift fuer Physik vol. 93, (1935) more especially Figs. 2-4 on pages 764/65. This invention is concerned with tubes in which the spherical central part m of the cathode serving for the reproduction, has a highly curved border part 1" joining it, which then passes into the anode tube a, eventually across a constricted part e with the plate cylinder z. The electron image is received on the fluorescent screen i.

In many cases such construction of the cathode is not desirable. In fact, the purpose of the curvature of the cathode is to provide for the potential surfaces in the vicinity of the cathode a convex curvature, in other words, the potential surfaces shall form an electron lens analogous to a concentrating lens, since we are concerned with an accelerating electrostatic field. However, the curvature of the cathode at the border thereof has the effect that the potential surfaces in the vicinity of the cathode have also their central region afiected. The invention provides a cathode structure in which this influence is controlled in another way, so that still more favorable conditions of reproduction are hereby provided.

According to the invention the cathode is formed as non-spherical surface of revolution I Whose special shape brings about the elimination of reproduction faults which would otherwise be present, and whereby the sharply reproduced area can be increased. According to a further feature of the invention, the cathode is. substantially a spherical surface, but the surrounding protection ring known as such and maintained at cathode potential is shaped accordingly as non-spherical surface of revolution. Thus cathode and protective ring form together the aspherical surface which is of advantage as regards reproduction.

In Fig. 2, k is the'cathode formed as a nonspherical surface of revolution in accordance with the invention, a is the plate cylinder. In Fig. 3, k is the cathode forming only the central area of the non-spherical surface of revolution, 8 is the protective ring, a is the anode cylinder. Appropriate. leads to the cathodes and anodes l5, l1, l9, 2i and 23 are shown in Figures 3 and 2 respectively for supplying potentials thereto.

Such cathode structure may obviously also be employed in reproducing systems other than those consisting only of cathode and anode, for instance, in systems in which still further charged electrodes (light stops, rings, cylinders or the like) or magnetic lenses are provided. In this case, however, this cathode structure has no particular advantage, since the necessary corrections of the reproducing field may then generally be achieved in a simpler manner, through suitable choice of the potentials, or of the coil current, arrangement of the electrodes, or coils, placing shielding caps over the coils and the like.

The reproducing system according to the invention can be applied wherever an' electron image is to be reproduced. The surface to be reproduced must not necessarily cover the central area but may also extend beyond the latter. Obviously, it should not reach to the part of the cathode forming a convex surface relative to the anode, such as indicated, for instance, in the example of construction of Fig. 2, but is to be limited to the area which is convex relative to the anode, in front of which only the concentrating action of the potential field exists. The cathode may be designed for instance as glow cathode or as photo-cathode for an image converter. the latter caseit will consist in general of metal and metal compounds deposited through evaporation on a correspondingly shaped glass surface, as in the case in the known imageconverter shown in Fig. 1. An image converter with the cathode shaped in accordance with the invention Inv is shown in Fig. 2 in which the reference letters have the above stated significance.

According to a further feature of the invention, the form of the part of the glass vessel carrying the cathode instead of being obtained by free blowing, is produced by means of a correspondingly formed mould on which the blow cap rests. Such method is especially suited for mass production, and assures accurate obtaining of the desired form.

What We claim is:

1. An electron image tube comprising a cylindrical envelope closed at each end, a luminescent screen deposited on one end, a layer of photosensitive material deposited on the other end, said other end having a non-spherical curved surface of revolution having both positive and negative radius of curvature, and an anode positioned intermediate the cathode and screen.

2. An electron image tube comprising a luminescent screen of predetermined area, a nonspherical curved surface of revolution having both positive and negative radius of curvature photosensitive cathode in register with said screen, the area of said cathode being substantially larger than the predetermined area of said screen, and an anode positioned intermediate said screen and cathode.

3. An electron image tube comprising a luminescent screen of predetermined area, a nonspherical curved surface of revolution photosensitive cathode in register with said screen, the area of said cathode being substantially smaller than the predetermined area of said screen, a guard ring electrode adjacent to and in register With the cathode, and an anode intermediate said guard ring and said screen.

ERNST BRUCI-IE. WALTER SCI-IAFFERNICHT. 

